The present invention is related to prosthetic heart valve replacement, and more particularly to devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves for deployment in a patient.
Prosthetic heart valves that are collapsible to a relatively small circumferential size can be delivered into a patient less invasively than valves that are not collapsible. For example, a collapsible valve may be delivered into a patient via a tube-like delivery apparatus such as a catheter, a trocar, a laparoscopic instrument, or the like. This collapsibility can avoid the need for a more invasive procedure such as full open-chest, open-heart surgery.
Collapsible prosthetic heart valves typically take the form of a valve structure mounted on a stent. There are two types of stents on which the valves structures are ordinarily mounted: self-expanding stents and balloon-expandable stents. To place such valves into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size.
When a collapsed prosthetic valve has reached the desired implant site in the patient (e.g., at or near the annulus of the patient's heart valve that is to be replaced by the prosthetic valve), the prosthetic valve can be deployed or released from the delivery apparatus and expanded to full operating size. For balloon-expandable valves, this generally involves releasing the entire valve, assuring its proper location, and then expanding a balloon positioned within the valve stent. For self-expanding valves, on the other hand, the stent automatically begins to expand as the sheath covering the valve is withdrawn.
In conventional delivery systems for self-expanding aortic valves, after the delivery system has been positioned for deployment, the annulus end of the valve is typically unsheathed and expanded into engagement with the valve annulus, while the aortic end of the valve remains sheathed. Once the annulus end of the valve has expanded, it may be determined that the valve needs to be repositioned in the patient's valve annulus. To accomplish this, a user (such as a surgeon or an interventional cardiologist) typically resheathes the annulus end of the valve, so that the valve can be repositioned while in a collapsed state. After the valve has been repositioned, the user can again unsheathe the valve for deployment.
Once a self-expanding valve has been fully deployed, it expands to a diameter larger than that of the sheath that previously retained the valve in the collapsed condition, making resheathing impossible, or difficult at best. In order for a user to be able to resheathe a partially-deployed valve, a portion of the valve must still be collapsed inside of the sheath.
Despite the various improvements that have been made to the collapsible prosthetic heart valve delivery process, conventional delivery devices, systems, and methods suffer from some shortcomings. For example, in conventional delivery devices for self-expanding valves, the valve may be held in a compartment of the device by the engagement of retention members on the stent with one or more retainers in the compartment. During deployment of the valve into the desired area (e.g., the valve annulus), the high frictional force produced during unsheathing of the valve may cause high axial forces to be applied directly to the stent retention members, which may damage or deform the stent struts that support the retention members.
There therefore is a need for further improvements to the devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves. Among other advantages, the present invention may address one or more of these needs.